The ultrastructure of penetrating stages of Babesia major infecting the ovary of Haemaphysalis punctata.

The ultrastructure of penetrating stages of Babesia major merozoites responsible for causing trans-ovarian infection of the tick Haemaphysalis punctata was studied. These merozoites were different from forms of other Babesia species previously described in the tick in that they were highly pleomorphic. Most of the organelles found in these forms were similar to those found in other stages: however, the apical complex was found to be very active. Micronemes were found to be predominant in the cytoplasm of these merozoites and a cytoplasmic projection anterior to the polar ring and bounded by concentric rings was visible. A polar ring with radiating ribs, and microtubules was present. It is thought that the apical complex of these merozoites plays an important role in assisting the parasite to infect the ovary of the tick.